Piton de la Fournaise , La Réunion :

The eruption begun on July 14 at 00:50 local time continues.After a rapid drop in its intensity on July 31, the volcanic tremor (indicator of surface eruptive intensity) has been decreasing steadily since 24 hours.This day at 15:30 (local time), its intensity is equivalent to about 16% of that observed at the beginning of eruption (Figure 1).

The decline in the eruptive torque is reflected on the ground by a decline in activity.During a survey conducted this morning by the OVPF, no projection was visible at the level of the eruptive cone (Figure 2).The main mouth active these days is now completely clogged.The second mouth, of smaller size, showed an extremely low level of magma with strong degassing.

At 10:30 am (local time), only a few casting arms were visible on the surface (Figure 3), the nearest being 520 meters from the eruptive cone, with the rest of the activity occurring in the lava tunnel.

At the level of the resurgences of lava, also called « ephemeral mouths », morphologies and phenomena characteristic of flows in tunnels were observed (numbers 1 to 8 in Figure 3):

1) Under the pressure of the lava circulating in the tunnel (overpressure linked to an increase in flow or a « plug downstream ») a hornito was built.The latter was no longer active during the observations of this morning.

2) In the axis of the hornito and in the middle of a pahoehoe lava field, a very channeled effluent of lava 20 meters long and 1 m wide shows that the tunnel was still active and a placetransit flows.

3) Two ephemeral mouths had recently opened at the roof of the tunnel just before the shot.

4-5-6) The longest flow observed this morning, was 220 m long, and was initiated by an ephemeral mouth located in the alignment of the points described previously. At the point where the free surface was the widest, the flow reached barely 10 meters (in 4); More downstream and definitely linked to a lower slope, the casting spread out with a texture on a leaf / aa (at 5) to its front (at 6). It should be noted that even if the surface at 5 and 6 were cooled, the core of the flow was always liquid as evidenced by the two red lobes visible on both sides of the front.

7-8) Two other tongues of lava from ephemeral mouths at 520 meters from the vent were visible. The extension of these two flows was limited, with a length of 50 and 180 m.

– No earthquakes have been recorded in the past 24 hours.– The trend recorded on deformation sensors, in particular GPS, at the top of the volcano, seems to register a resumption of inflation again. This parameter will be followed in the next few days.

Estimates carried out using satellite methods via the HOTVOLC platform (OPGC – Clermont Ferrand) show a minimum flow rate of less than 1 m3 / s.

Source :OVPF

Photo :Da Latra

Yellowstone , United – States :

During July 2017, the University of Utah Seismograph Stations, responsible for the operation and analysis of the Yellowstone Seismic Network, reports 528 earthquakes were located in the Yellowstone National Park (YNP) region. The largest event was a minor earthquake of magnitude 3.6 on July 18, at 02:31 PM MDT, located about nine miles north northeast of West Yellowstone, MT. The earthquake was reported felt in the town of West Yellowstone, MT. This earthquake is part of a continued energetic sequence of earthquakes in the same area that began on June 12.

July seismicity in Yellowstone was marked by the ongoing seismicity ~six miles north of West Yellowstone, MT where an energetic swarm added an additional 475 earthquakes in July to the 1028 earthquakes in June. The swarm includes the largest event of the month on July 18 (magnitude 3.6). Swarm activity for July consists of two earthquakes in the magnitude 3 range and 40 earthquakes in the magnitude 2 range. Including the events from last month beginning on June 12, total swarm seismicity includes one earthquake of magnitude 4.4, seven in the magnitude 3 range, and 112 earthquakes in the magnitude 2 range.

Earthquake sequences like these are common and account for roughly 50% of the total seismicity in the Yellowstone region.

Yellowstone earthquake activity is currently at elevated levels compared with typical background activity.

Ground deformation

Monitored locations within the Yellowstone Caldera show minimal change this month. Uplift north of the caldera, centered near the Norris Geyser Basin continues at a low rate. Behavior is similar to the past several months. Current deformation patterns at Yellowstone remain within historical norms.

The Yellowstone Volcano Observatory (YVO) provides long-term monitoring of volcanic and earthquake activity in the Yellowstone National Park region. Yellowstone is the site of the largest and most diverse collection of natural thermal features in the world and the first National Park. YVO is one of the five USGS Volcano Observatories that monitor volcanoes within the United States for science and public safety.

Source : HVO.

Nevado Del Ruiz , Colombia :

Weekly activity bulletin of the volcano Nevado del Ruiz, from 25 July to 31 July 2017.The level of activity continues: at the level of yellow (III) activity: changes in the behavior of volcanic activity.

As regards the monitoring of the activity of the Nevado del Ruiz volcano, the Colombian Geological Survey reports that:

Over the past week, the various monitoring parameters indicate that the Nevado del Ruiz volcano continues to exhibit unstable behavior.

The seismicity caused by fracturing of the rocks that makes up the volcano, showed a slight increase in the number of earthquakes and seismic energy released compared to the previous week. The earthquakes were mostly in the Northeast Sector, the Southwest Sectors near the Arenas Crater, and to a lesser extent in the Southeast and North distal areas at depths between 0.62 and 6 , 96 km. The maximum magnitude recorded during the week was 0.7 ML (local magnitude), which corresponds to two earthquakes recorded on July 25 at 14:30 (local time), located in the Arenas crater at a depth of 0 , 71 km and July 27 at 14h13 (local time), located in the Northeast sector at a depth of 3.4 km.

The seismic activity associated with fluid dynamics within the volcanic structure showed a decrease in the number of recorded earthquakes and the seismic energy released during the previous week. This type of activity is mainly characterized by the occurrence of several seismic events of long period and very long period fluids and tremor pulses of varying energy levels and durations.

Volcanic deformation, measured from electronic inclinometers, Global Navigation Satellite Systems (GNSS) and satellite imagery to determine changes in inclination, position and shape of the volcano, continues to record over A deflationary process.

In the tracking information provided by the NASA and FIRMES Mírová website, no thermal anomaly was identified during the week.

The columns of gas and steam reached a maximum height of 350 m measured on top of the volcano on July 25th.